The use of magnesium salts and magnesium surfactants in dishwashing detergent formulations is taught in the patent literature and the disclosures of British Pat. Specifications Nos. 1,524,441 and 1,551,074 and British published Patent Application No. 2,010,893 A are representative of the state of the art. The art teaches that these formulations have enhanced performance, particularly when used in water of low mineral hardness. Nevertheless products made in accordance with these teachings have all been found to be non-optimum in various ways such as raw material expense, phase stability on storage, performance in hard water, effect on hands and suds profile.
Accordingly the search has continued for compositions having improved economy, performance and in use characteristics and it has now been found that certain combinations of active ingredients can provide a range of enhanced properties not thought previously attainable in one formulation. More particularly it has been found possible to provide concentrated stable liquid dishwashing formulations of improved greasy soil removal, suds profile, viscosity and freeze-thaw characteristics.
The Applicants have found that compositions incorporating a ternary anionic surfactant mixture comprising alkyl benzene sulphonate, alkyl ether sulphate and alkyl sulphate, and in which part of the cation system is magnesium, produce the maximum suds mileage, i.e. number of dishes washed) when the magnesium level corresponds to the level of alkyl sulphate present.
Furthermore, in one aspect of the invention, it has been found possible to combine these characteristics with no sacrifice in the effect on hands relative to leading liquid dishwashing detergents available commercially.
An additional increment of sudsing performance is obtainable by the addition of a suds booster such as an alkyl alkanolamide. It had previously been believed that high levels of performance could only be obtained by the use of very high surfactant levels or by the use of high levels of suds boosters, which were expensive, difficult to incorporate and gave rise to phase stability problems on storage. The Applicants have found that surprisingly low suds booster levels viz. 3-4% provide a significant sudsing benefit in the formulations of the present invention and that, whilst levels of 6-8% can be used they offer little or no performance advantages over the lower levels.
Whilst the mechanism by which the compositions of the invention attain their enhanced performance is not fully understood and whilst the Applicants do not wish to be bound by any theory, it is believed that, in the ternary surfactant system employed in the compositions, magnesium is primarily associated with the alkyl sulphate in a polar ie. non-ionic bond arrangement and that this combination of the magnesium and alkyl sulphate, provides a more closely packed (and hence stable) structure in the suds. The effect of any additional suds booster is believed to be primarily of a suds-stabilising nature.